1. Field of the Invention
The present invention generally relates to an ultrasonic imaging method and an ultrasonic imaging apparatus to be used in diagnosing organs existing in a biological body, or in performing nondestructive tests. More specifically, the present invention is directed to such an ultrasonic imaging method and ultrasonic imaging apparatus capable of obtaining image information in high frame rates, and/or capable of improving resolution of obtained image information.
2. Description of a Related Art
Normally, in ultrasonic imaging apparatuses utilized as ultrasonic diagnostic apparatuses or industrial-purpose defect (flaw) detecting apparatuses, ultrasonic probes are employed each contains a plurality of ultrasonic transducers and has ultrasonic transmission/reception functions. In one typical ultrasonic imaging apparatus equipped with such an ultrasonic probe, image information related to an object to be inspected may be obtained in such a manner that this object to be inspected is ultrasonically scanned by using ultrasonic beams, while the ultrasonic beams are produced by synthesizing ultrasonic waves transmitted from the plurality of ultrasonic transducers. Then, the ultrasonic imaging apparatus may reproduce either two-dimensional regional images or three-dimensional regional images of the object to be inspected based upon the obtained image information. As one of scanning methods of scanning an object to be inspected by way of such ultrasonic beams, so-called xe2x80x9csector scanning operationxe2x80x9d is carried out by which a two-dimensional fan-shaped region is ultrasonically scanned along angular directions.
Originally, this sector scanning method has been developed as a method of observing cardiac portions (hearts) of biological bodies (human bodies) from intercostal portions thereof. In such a sector scanning method, an object to be inspected is scanned in an equi-interval along angular directions one after another by employing ultrasonic beams which are transmitted from a transmission point into the object to be inspected along a depth direction. Furthermore, image information is sampled at a plurality of sampling points one after another. These sampling points are distributed in the equi-interval along the depth direction of the object to be inspected along the ultrasonic beams at the respective angles. As described above, while one ultrasonic beam is used to scan an object to be inspected, image information related to a plurality of sampling points located on this single ultrasonic beam is sampled at predetermined time intervals. Either a two-dimensional image or a three-dimensional image as to a cardiac portion (heart), which are obtained from the sampled image information, is called as an echocardiogram.
With respect to such sector scanning methods, two major scanning methods have been mainly known, namely a mechanical sector scanning method and an electronic sector scanning method.
According to the mechanical scanning method, a sector scanning operation is performed in such a manner that an ultrasonic probe is mechanically and pivotally moved by way of an oscillation motion, a swing motion, and the like.
According to the electronic scanning method, an ultrasonic probe constituted by arraying several tens of small-sized ultrasonic transducer elements is employed, and time differences are defined in timing for driving the respective ultrasonic transducer elements so that the ultrasonic transducer element group is equivalently driven in the swing motion.
On the other hand, currently, more correct and objective ultrasonic diagnostic methods are requested in medical fields. Under such circumstances, specific attentions are paid to imaging methods of real-time three-dimensional echocardiography capable of easily understanding three-dimensional structures of hearts. For example, please see Japanese publication entitled xe2x80x9cTREND TO REAL-TIME THREE-DIMENSIONAL ECHOCARDIOGRAPHYxe2x80x9d written by T. OHTA, EIZO JYOHO (M) Vol. 32, No. 22, pp. 1248-1254, published in November, 2000.
Conventionally, the below-mentioned imaging methods are known as the three-dimensional echocardiography imaging method:
(1) An imaging method in which a plurality of two-dimensional tomographic echocardiograms of an object to be inspected are stored by slowly moving an one-dimensional probe in a mechanical scanning manner by an operator, and then, these two-dimensional tomographic echocardiograms are displayed as a three-dimensional echocardiogram.
(2) An imaging method in which three-dimensional image information of an object to be inspected is obtained by performing an electronic scanning operation along one direction and also a mechanical scanning operation along another direction.
(3) An imaging method in which an object to be inspected is electronically scanned along two directions by employing a sparse two-dimensional ultrasonic sensor. This sparse two-dimensional ultrasonic sensor corresponds to such a sensor that some transducers are selectively used among transducers arrayed in a two-dimensional matrix form constituted by N columnsxc3x97N rows.
However, the three-dimensional echocardiography imaging method (1) owns the following drawbacks. That is, the one-dimensional probe must be manipulated by skilled operators, and also, lengthy time is required to obtain the desirable image information. Also, according to the imaging method (2), the desirable image information can be obtained within shorter time than that in the first-mentioned imaging method (1). However, the frame rate (namely, total number of images displayed on display screen per unit time) is lower than, or equal to 20 frames per second, which can be hardly regarded as a high frame rate. Furthermore, according to the imaging method (3), the frame rate is lower than, or equal to 20 frames per second, which can also be hardly regarded as a high frame rate.
The present invention has been made to solve the above-described problems, and therefore, has an object to provide improved ultrasonic imaging method and apparatus capable of obtaining image information in a high frame rate or capable of increasing resolution by increasing a total number of ultrasonic beams which can be transmitted within unit time.
To solve the above-described problems, an ultrasonic imaging method according to one aspect of the present invention, of transmitting an ultrasonic beam toward a measurement target located within an object to be inspected, receiving an ultrasonic echo reflected from the measurement target and processing detection signals so as to obtain image information of the measurement target, comprises the steps of: (a) executing a pre-imaging operation and setting a region with respect to the measurement target on the basis of an image obtained by the pre-imaging operation; and (b) transmitting an ultrasonic beam in such a manner that the region set in step (a) is scanned and receiving an ultrasonic echo so as to execute an ultrasonic imaging operation.
Also, an ultrasonic imaging apparatus according to one aspect of the present invention, for transmitting an ultrasonic beam toward a measurement target located within an object to be inspected, receiving an ultrasonic echo reflected from the measurement target and processing detection signals so as to obtain image information of the measurement target, comprises: drive signal generating means for generating a plurality of drive signals; an ultrasonic probe for transmitting an ultrasonic beam in accordance with the drive signals generated by the drive signal generating means and receiving an ultrasonic echo which is produced by the transmitted ultrasonic beam to output a plurality of detection signals; signal processing means for obtaining image information of the measurement target on the basis of the plurality of detection signals output from the ultrasonic probe; measurement region setting means to be used for setting a region with respect to the measurement target; and control means for controlling both the drive signal generating means and the signal processing means to transmit the ultrasonic beam and receive the ultrasonic echo by using the ultrasonic probe in such a manner that the region set by the measurement region setting means is scanned.
In accordance with the ultrasonic imaging method and apparatus of the present invention, since the measuring time is shortened and a number of times of transmission/reception operations of the ultrasonic beam per unit time is increased, the imaging operation can be carried out with maintaining high frame rates or high resolution.